Hard carbons are among the most promising anode materials for Na-ion batteries (NIB) and are extensively studied. Nevertheless, it is still necessary to decipher the electrochemical intercalation behavior of sodium which is still under debate in the literature. Here, we present an innovating approach for elaborating hard carbon from simple sucrose precursor. It consists in a low-temperature pyrolysis at 500 °C under controlled argon pressure, followed by low-temperature carbonization. Using complementary characterization techniques (XRD, Raman, TEM, gas adsorption, SAXS) and galvanostatic electrochemical measurements, we show that this elaboration route allows the possibility to control and modify the porosity of the hard carbons without any modification of the structure of the material. This work leads us to assign the low potential plateau to the development of quasimetal clustering of sodium into narrow porosity developed tuned thanks to the pyrolysis under pressure.